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Digital Circuit Boards: Mach 1 GHz by Ralph Morrison

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5.18 Glossary

Apertures (Section 5.16): Any opening that allows electromagnetic energy to enter a conductive enclosure. There is no attenuation of an external field (worst case) when the aperture's maximum dimension is one-half the wave length. The field attenuation for a smaller opening is the ratio of half wave length to aperture opening.

Apertures that are spaced so that surface currents can circulate freely around the aperture are independent. The field penetration for several independent apertures is additive. Dependent apertures such as screens, seams, or ventilation arrays act as one aperture.

Coax: See shielded cable.

Common (Section 5.11): A term used to mean ground or the conductor at zero volts. This conductor is sometimes called the reference conductor. Terms such as signal common, output common, digital common, and power supply common are often used.

Cross coupling/cross talk (Section 5.4): The coupling of wave energy from one trace to a nearby trace. The coupling involves both forward and reverse traveling waves. Coupling only occurs where the wave amplitude is in transition. Reverse wave coupling causes most interference problems. The amplitude depends on rise time. The reverse wave lasts twice as long as the coupling time. The forward coupled wave is a pulse that increases in amplitude with time. Forward coupling is apt to be a problem on long outer traces.

Embedded microstrip (Section 5.6): The outer layer traces are covered by a dielectric. These traces are not ...

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